Wet-process phosphoric acid contains a significant amount of uranium, typically about 0.1 to 0.2 g/l. Apart from being economically favourable, the recovery of uranium as a by-product of phosphate fertilizer production supplies part of the world's nuclear fuel resource and reduces the environmental contamination. In order to recover the valuable source of uranium, a so-called "D.sub.2 T-D.sub.2 T process" has been developed by a research team at the Oak Ridge National Laboratory in the United States to separate it from a phosphoric acid solution prior to further treatment to produce a fertilizer product. (See U.S. Pat. No. 3,711,591 by F. J. Hurst et al. titled "Reductive Stripping Process for the Recovery of Uranium from Wet-process Phosphoric Acid". Also, see the article in Ind. Eng. Chem. Process Des. Develop., 11, 122 (1972) by F. J. Hurst et al. titled "Recovery of Uranium from Wet-process Phosphoric Acid").
The D.sub.2 T-D.sub.2 T process comprises two steps. A synergistic extractant combination consisting of di(2-ethylhexyl) phosphoric acid (D2EHPA) and trioctylphosphine oxide (TOPO) in kerosene is used in this process to extract uranium in the +6 oxidation state in the first step. In the second step of the process, the concentrated acidic aqueous stream is again oxidated and extracted with the same synergistic organic extractant, and finally stripped with ammonium carbonate solution to precipitate ammonium uranyl tricarbonate, (NH.sub.4).sub.4 UO.sub.2 (CO.sub.3).sub.3, (AUT).
This process typically suffers from several disadvantages: (1) The TOPO synergistic agent is expensive and hence the total chemical reagent cost is higher. (2) In the second purification part of D.sub.2 T-D.sub.2 T process, the use of ammonium carbonate as the stripping reagent results in the conversion of the D2EHPA to a highly hydrated ammonium salt, ##STR1## When the stripped solvent is recycled to the extraction step, the extracted water and NH.sub.4.sup.+ transfer to the aqueous phosphoric phase, dilute and contaminate the wet-process phosphoric acid, which is unacceptable to the phosphoric acid plant to produce feed stocks and various phosphate chemicals. These in turn have some other disadvantageous effects such as unclear phase separation, ammonium salt precipitation [Fe.sub.3 NH.sub.4 H.sub.8 (PO.sub.4).sub.6.6H.sub.2 O etc.] and cause problems during operation.